1. Technical Field
The present invention relates to energetic materials in general, and, in particular, to a method for manufacturing energetic material composites.
2. Description of Related Art
Theoretically, aluminum and water react exothermically to form aluminum oxide and hydrogen gas:2Al(s)+3H2O(l)→Al2O3(s)+3H2(g)ΔH=−818 kJIt is a very energetic chemical reaction capable of generating 7.6 kJ of energy per gram of reactants (i.e., aluminum and water). The combination of hydrogen's relatively low molecular weight and the high energy generated from the chemical reaction allows hydrogen gas to be released at a very high average speed during chemical reactions. This property makes the above-mentioned reaction pair desirable as a propellant formulation.
In practice, however, aluminum and water are rarely used together as an energetic material. This is because the energy release rate of the chemical reaction between aluminum and water is very slow unless aluminum is in the form of very fine particles. For example, it is quite difficult to ignite aluminum powder of approximately 5 microns in diameter (which are considered as fine particles) mixed stoichiometrically with water because the mixture often self-extinguishes due to low reaction rate.
When very fine aluminum particles are used, the reaction rate increases to the point of mimicking a very fast burning propellant. The size of very fine aluminum particles is usually below 200 nm in diameter (i.e., 11 m2/g if the particles are spherical). This type of very fine aluminum particles is commonly referred to as nanoaluminum powder or nanoaluminum. The problem with nanoaluminum is that it is unstable in water even at room temperature. At 25° C., 80 nm diameter (i.e., 28 m2/g) nanoaluminum particles in deionized water will begin to react with the water, such as generating hydrogen gas bubbles, within a few minutes of mixing.